Epoxy systems may be categorized into two-part systems and one-part systems. In two-part systems, an epoxy resin “part” is maintained separate from a curative “part” to prevent premature curing of the epoxy resin. Some type of mechanical action (i.e., mixing, extrusion, etc.) must take place to combine the components of the two-part epoxy system so that a curing step can be initiated, often accompanied with either light and/or heat. Two-part epoxy systems have limited applicability in finished products, such as adhesive tapes, due to the need to physically separate the system components from one another.
In one-part epoxy systems, an epoxy resin is combined with a curative to form a single composition, which cures upon exposure to light and/or heat. One-part epoxy systems have an advantage over two-part systems in that the one-part epoxy system can be utilized in a number of products without the need to separate individual components of the system. One-part epoxy systems find utility in a number of applications including, but not limited to, adhesives, adhesive tapes, film adhesives, etc. The uncured product may be positioned as desired in a given application, and then subsequently cured by the application of energy, e.g., light and/or heat, without the need to combine additional components to the epoxy system.
Shelf life is an important parameter for epoxy-based compositions and products made therefrom, especially compositions and products formed from one-part epoxy systems. Over time, one-part epoxy compositions and products made therefrom can experience undesirable properties, such as premature reaction between components of the epoxy system. The premature reaction causes an increase in viscosity over time, which results in decreased flow of the composition. In some applications, such as sealing joints and seams in an automobile body, a sealant composition needs to be able to flow sufficiently to fill openings between seams and seal the joint to prevent water and moisture from leaking into the vehicle.
What is needed in the art is an epoxy composition having improved shelf life. What is also needed in the art is an adhesive or melt-sealing tape formed from an epoxy composition having improved shelf life, and in particular, a composition that does not increase significantly in viscosity over time.